The present invention relates to a selective temperature control system for use in a space cooling device, such as a room air conditioner, in which the compressor energization and the fan speed are adjusted automatically in response to the difference between the ambient temperature and a set point temperature.
In many air conditioning systems, the compressor motor and evaporator fan motor are variable in speed by using a user-set control potentiometer and a feedback circuit which senses the motor speeds. Such systems are responsive to temperature sensors or thermostats to vary the compressor motor speed and the evaporator fan speed.
In some prior art systems, to protect the evaporator coils from freezing and also to sense the ambient temperature, a vapor bulb thermostat has been mounted on a plastic block which in turn is mounted on the evaporator coils so as to sense both the evaporator temperature and the ambient temperature. However, such attempts to sense both temperatures using only one sensor results in large temperature swings within the cooled room because of the mixing of the evaporator and ambient temperatures.
Some air conditioning controls also employ the use of a compressor lockout, which is designed to prevent the compressor from short cycling and from locking up. Often this is achieved by the use of a timer which insures that the compressor will remain off for a predetermined amount of time. Other systems employ the use of a percentage timer which insures that the compressor is off for a fixed percentage of time within a complete compressor cycle.